1. Field of the Invention
The present invention is directed to an improved surge attenuating baffle for collapsible liquid storage tanks, and more particularly, to an improved baffle for collapsible liquid storage tanks which provide substantially instantaneous surge attenuation as soon as a surge of liquid is in development in the storage tank.
2. Description of the Prior Art
Pillow tanks, i.e., collapsible self-supporting and transportable storage tanks, have been used for a long time in land based installations. Pillow tanks are usually fabricated from rubberized fabric or like material. A principal advantage of the pillow tanks is that, when empty, they are relatively light-weight and, therefore, are readily transportable, particularly in a rolled-up state.
For a long time, however, transportation of a pillow tank partially or entirely filled with a liquid presented an almost insurmountable problem because of surges developing in the liquid contained in the tank. The surges in the transported liquid are invariably occasioned by the acceleration or deceleration of the vehicle transporting the pillow tank. As it is readily appreciated by those skilled in the art, liquid surges which may develop in a pillow tank transported in a truck and particularly in an aircraft, if unattenuated, may reach destructive proportions. Experience has shown that substantially unattenuated surges of liquid developing in a pillow tank transported in an aircraft may even lead to total loss of control and resultant crash of the aircraft.
U.S. Pat. No. 3,288,186 in its introductory portion describes in detail the difficulties encountered in the prior art in attempting to adapt pillow tanks for transportation and especially airborne transportation of liquids. The introductory portion of that patent disclosure explains that surges in the liquid reach particularly dangerous proportions when a transported pillow tank is in a partially empty state.
As a solution to the above summarized problem, U.S. Pat. No. 3,288,186 discloses a surge attenuating baffle and pillow tank combination which finally rendered possible the airborne transportation of liquids in full, and more importantly, in partially filled pillow tanks. As is readily appreciated, airborne transportation of liquids such as hydrocarbon fuels in partially filled containers has special importance in certain types of military operations wherein, e.g. several bases must be supplied with varying amounts of fuel from the same pillow tank.
Briefly, the baffle disclosed in U.S. Pat. No. 3,288,186 comprises a plurality of flexible, elongated, tapered pockets having opposite open ends. The pockets are disposed with their respective elongate extents substantially parallel with the direction of the surge of liquid in an elongate pillow tank. A base strip is directly secured circumferentially to the interior surface of the pillow tank transversely to the length of the tank. A baffle strip is then secured by grommets and laces to the base strip along regularly spaced alternatively converging and diverging lines on the base strip so that the pockets in their fully extended state have subtantially semicircular cross sections.
The baffle strip of the device described in U.S. Pat. No. 3,288,186 is a flexible strip made of a single sheet or single ply of suitable rubberized material. The flexible baffle strip allows the pillow tank to collapse when liquid is withdrawn from the tank, and even permits storage of the pillow tank in a substantially flat or "rolled-up" state.
Although the baffle strip of U.S. Pat. No. 3,288,186 has been successfully used for several years for airborne transportation of fuel, it has a disadvantage in that the pockets or convolutions which attenuate the liquid surges in the tank, are usually in a collapsed state when the liquid is at rest in the tank. Therefore, at least some initial movement of the surging liquid is required before the baffle reaches its intended "multiple-pocket" like configuration and becomes effective in attenuating the surge of the liquid in the tank.
In summary, the baffle disclosed in U.S. Pat. No. 3,288,186 works well. Nevertheless, its less than instantaneous ability to attenuate a developing surge has placed an upper limit on the size of transportable and particularly airborne pillow tanks which may be built in accordance with the teachings of U.S. Pat. No. 3,288,186. Generally speaking, it was thought to be unpractical to build transportable pillow tanks capable of holding more than approximately three thousand gallons of liquid. As an improvement over the teachings of U.S. Pat. No. 3,288,186, the present invention provides a baffle having instantaneous surge attenuating ability and, therefore, renders possible the manufacture of larger than three thousand gallon pillow tanks and transportation of liquids in the same.